Periodic Reporting for period 2 - ECLIPSE (Exotic superconducting CIrcuits to Probe and protect quantum States of light and mattEr)
Okres sprawozdawczy: 2021-09-01 do 2023-02-28
Quantum systems can occupy peculiar states, such as superposition or entangled states. These states are intrinsically fragile and eventually get wiped out by inevitable interactions with the environment. Protecting quantum states against decoherence is a formidable and fundamental problem in physics, which is pivotal for the future of quantum computing. The theory of quantum error correction provides a solution, but its current envisioned implementations require daunting resources: a single bit of information is protected by encoding it across tens of thousands of physical qubits.
Project ECLIPSE aims to protect quantum information in an entirely new type of qubit coined the cat-qubit with two key specificities. First, it will be encoded in a single superconducting circuit resonator whose infinite dimensional Hilbert space can replace large registers of physical qubits. Second, this qubit will be rf-powered, continuously exchanging photons with a reservoir. This approach challenges the intuition that a qubit must be isolated from its environment. Instead, the reservoir acts as a feedback loop which continuously and autonomously corrects against errors. This correction takes place at the level of the quantum hardware, and reduces the need for error syndrome measurements which are resource intensive.
Project ECLIPSE aims to protect quantum information in an entirely new type of qubit coined the cat-qubit with two key specificities. First, it will be encoded in a single superconducting circuit resonator whose infinite dimensional Hilbert space can replace large registers of physical qubits. Second, this qubit will be rf-powered, continuously exchanging photons with a reservoir. This approach challenges the intuition that a qubit must be isolated from its environment. Instead, the reservoir acts as a feedback loop which continuously and autonomously corrects against errors. This correction takes place at the level of the quantum hardware, and reduces the need for error syndrome measurements which are resource intensive.
Since the beginning of the project in March 2020, we have:
• Built a new lab space: We have built a new lab space at ENS Paris in order to host the experiments from project ECLIPSE.
• Installed a new dilution refrigerator: Using funds from project ECLIPSE, we have ordered a new dilution refrigerator from Bluefors, wired it and it is up and running. It has 24 RF inputs, 6 RF outputs, 36 twisted pairs to base, and 12 twisted pairs to the 4K stage. We have equipped it with all the necessary RF and DC filtering, amplification and attenuation necessary to perform state of the art experiments. We have designed custom parts for magnetic shielding, brackets and sample holders.
• Hired a team of scientists: We have hired a great team of 6 PhD students and 1 postdoc working on this project. Some of them are paid by the ECLIPSE funds, but most have complementary funding.
• Published in PRX: “Magnifying Quantum Phase Fluctuations with Cooper-Pair Pairing” by W. C. Smith, M. Villiers, A. Marquet, J. Palomo, M. R. Delbecq, T. Kontos, P. Campagne-Ibarcq, B. Douçot and Z. Leghtas. PRX 12, 021002 (2022).
• Preprint on the arXiv:2204.09128 “One hundred second bit-flip time in a two-photon dissipative oscillator” by C. Berdou, A. Murani, U. Reglade, W. C. Smith, M. Villiers, J. Palomo, M. Rosticher, A. Denis, P. Morfin, M. Delbecq, T. Kontos, N. Pankratova, F. Rautschke, T. Peronnin, L.-A. Sellem, P. Rouchon, A. Sarlette, M. Mirrahimi, P. Campagne-Ibarcq, S. Jezouin, R. Lescanne and Z. Leghtas.
• Preprint on the arXiv:2212.04991: “Dynamically enhancing qubit-photon interactions with anti-squeezing” by M. Villiers, W. C. Smith, A. Petrescu, A. Borgognoni, M. Delbecq, A. Sarlette, M. Mirrahimi, P. Campagne-Ibarcq, T. Kontos, Z. Leghtas.
• Built a new lab space: We have built a new lab space at ENS Paris in order to host the experiments from project ECLIPSE.
• Installed a new dilution refrigerator: Using funds from project ECLIPSE, we have ordered a new dilution refrigerator from Bluefors, wired it and it is up and running. It has 24 RF inputs, 6 RF outputs, 36 twisted pairs to base, and 12 twisted pairs to the 4K stage. We have equipped it with all the necessary RF and DC filtering, amplification and attenuation necessary to perform state of the art experiments. We have designed custom parts for magnetic shielding, brackets and sample holders.
• Hired a team of scientists: We have hired a great team of 6 PhD students and 1 postdoc working on this project. Some of them are paid by the ECLIPSE funds, but most have complementary funding.
• Published in PRX: “Magnifying Quantum Phase Fluctuations with Cooper-Pair Pairing” by W. C. Smith, M. Villiers, A. Marquet, J. Palomo, M. R. Delbecq, T. Kontos, P. Campagne-Ibarcq, B. Douçot and Z. Leghtas. PRX 12, 021002 (2022).
• Preprint on the arXiv:2204.09128 “One hundred second bit-flip time in a two-photon dissipative oscillator” by C. Berdou, A. Murani, U. Reglade, W. C. Smith, M. Villiers, J. Palomo, M. Rosticher, A. Denis, P. Morfin, M. Delbecq, T. Kontos, N. Pankratova, F. Rautschke, T. Peronnin, L.-A. Sellem, P. Rouchon, A. Sarlette, M. Mirrahimi, P. Campagne-Ibarcq, S. Jezouin, R. Lescanne and Z. Leghtas.
• Preprint on the arXiv:2212.04991: “Dynamically enhancing qubit-photon interactions with anti-squeezing” by M. Villiers, W. C. Smith, A. Petrescu, A. Borgognoni, M. Delbecq, A. Sarlette, M. Mirrahimi, P. Campagne-Ibarcq, T. Kontos, Z. Leghtas.
• Magnifying Quantum Phase Fluctuations with Cooper-Pair Pairing (PRX 2022)
We have demonstrated that a new type of junction – that allows only pairs of Cooper pairs to tunnel – significantly increases the spread of the circuit wavefunction across multiple Josephson wells. This has important implications for (i) performing fault-tolerant error syndrome measurements for cat-qubits and (ii) building a new type of qubit, entirely protected from decoherence at the Hamiltonian level.
• One hundred second bit-flip time in a two-photon dissipative oscillator (arXiv:2204.09128)
This experiment has shown that by circumventing all suspected sources of dynamical instabilities, and removing the transmon qubit usually employed for quantum tomography, the bit-flip time rises exponentially with photon number for an extra 6 orders of magnitude before hitting a plateau at 100 seconds. This work therefore points towards a transmon-free cat-qubit architecture. The next milestone will be that the ability to prepare and measure quantum superposition states - absent in this experiment - is recovered.
• Dynamically enhancing qubit-photon interactions with anti-squeezing arXiv:2212.04991
The interaction strength of an oscillator to a qubit grows with the oscillator's vacuum field fluctuations. The well-known degenerate parametric oscillator has revived interest in the regime of strongly detuned squeezing, where its eigenstates are squeezed Fock states. Owing to these amplified field fluctuations, it was recently proposed that squeezing this oscillator would dynamically boost qubit-photon interactions. In this experiment, we observe a two-fold increase in the dispersive interaction between a qubit and an oscillator at 5.5 dB of squeezing, demonstrating in-situ dynamical control of qubit-photon interactions. This work initiates the experimental coupling of oscillators of squeezed photons to qubits, and cautiously motivates their dissemination in experimental platforms seeking enhanced interactions.
Expected results: We expect to observe a cat-qubit with bit-flip times beyond 1 second, and phase-flip times of about one microsecond. From there, we will start scaling to two, then three, then five cat-qubit chains. In parallel, we expect to construct a superconducting qubit based on Cooper-pair pairing that is intrinsically protected from decoherence, aiming for about 10 millisecond coherence times.
We have demonstrated that a new type of junction – that allows only pairs of Cooper pairs to tunnel – significantly increases the spread of the circuit wavefunction across multiple Josephson wells. This has important implications for (i) performing fault-tolerant error syndrome measurements for cat-qubits and (ii) building a new type of qubit, entirely protected from decoherence at the Hamiltonian level.
• One hundred second bit-flip time in a two-photon dissipative oscillator (arXiv:2204.09128)
This experiment has shown that by circumventing all suspected sources of dynamical instabilities, and removing the transmon qubit usually employed for quantum tomography, the bit-flip time rises exponentially with photon number for an extra 6 orders of magnitude before hitting a plateau at 100 seconds. This work therefore points towards a transmon-free cat-qubit architecture. The next milestone will be that the ability to prepare and measure quantum superposition states - absent in this experiment - is recovered.
• Dynamically enhancing qubit-photon interactions with anti-squeezing arXiv:2212.04991
The interaction strength of an oscillator to a qubit grows with the oscillator's vacuum field fluctuations. The well-known degenerate parametric oscillator has revived interest in the regime of strongly detuned squeezing, where its eigenstates are squeezed Fock states. Owing to these amplified field fluctuations, it was recently proposed that squeezing this oscillator would dynamically boost qubit-photon interactions. In this experiment, we observe a two-fold increase in the dispersive interaction between a qubit and an oscillator at 5.5 dB of squeezing, demonstrating in-situ dynamical control of qubit-photon interactions. This work initiates the experimental coupling of oscillators of squeezed photons to qubits, and cautiously motivates their dissemination in experimental platforms seeking enhanced interactions.
Expected results: We expect to observe a cat-qubit with bit-flip times beyond 1 second, and phase-flip times of about one microsecond. From there, we will start scaling to two, then three, then five cat-qubit chains. In parallel, we expect to construct a superconducting qubit based on Cooper-pair pairing that is intrinsically protected from decoherence, aiming for about 10 millisecond coherence times.